INTENSITY MODULATION TECHNIQUE

SUBMITTED BY:R ASHOK KUMAR(ECE-2, 25013202810)GAURAV MITHAS(ECE-2, 14513202810)

AMIT SHARMA(ECE-2,

SOURABH KUMAR(ECE-2, 13613202810)

CONTENTS• MODULATION• MODULATION TECHNIQUES• INTENSITY MODULATION• TYPES OF INTENSITY MODULATION• APPLICATION OF INTENSITY

MODULATION

Modulation is the process of varying one or more properties of the carrier signal with a modulating signal which typically contains information to be transmitted.

MODULATION

MODULATION TECHNIQUES

INTENSITY MODULATION

• IM: Optical power output of a source is varied in accordance with some characteristic of the modulating signal.

• No discrete upper and lower sidebands as optical sources lack sufficient coherence to produce them.

• Recovery of the modulating signal is by direct detection, not heterodyning.

TYPES OF INTENSITY MODULATION Direct intensity modulation(D-IM)

Subcarrier intensity modulation(S-IM) Subcarrier amplitude modulation(AM-IM) Subcarrier frequency modulation(FM-IM) Subcarrier phase modulation(PM-IM)

Subcarrier double sideband modulation

(DSB-IM)

Pulse analog techniques Pulse amplitude modulation(PAM-IM) Pulse width modulation(PWM-IM) Pulse frequency modulation(PFM-IM)

DIRECT INTENSITY MODULATION

• Simplest form of analog modulation for optical fiber communications.

• The optical output from the source is modulated simply by varying the current flowing in the device around a suitable bias or mean level in proportion to the message.

• No electrical modulation or demodulation is required hence, both inexpensive and easy to implement.

Fig (a) Analog optical fiber system employing direct intensity modulation. (b) Time domain representation showing direct intensity modulation of the optical carrier with a baseband analog signal

SUBCARRIER INTENSITY MODULATION(S-IM)

• Used for wideband signals.

• Number of baseband channels are multiplexed onto a single fiber link.

• Provides improvement in SNR.

• TYPES:FM–IMPM–IM

Fig. Subcarrier intensity modulation system for analog optical fiber transmission

Subcarrier frequency modulation(FM-IM)• The subcarrier is frequency modulated by the

modulating signal.

Subcarrier phase modulation(PM-IM)• The instantaneous phase of the subcarrier is

set proportional to the modulating signal.

SUBCARRIER DOUBLE SIDEBAND MODULATION(DSB-IM)

• Spectrum translated by direct multiplication of the baseband message signal with the subcarrier.

• frequency domain representation show only two sideband components.

• Provides 3 dB degradation in SNR.

• Considered inefficient.

Fig. Time and frequency domain representations of double-sideband modulation

PULSE ANALOG TECHNIQUES

• Pulse analog techniques employ pulse modulation in the electrical regime prior to intensity modulation of the optical source.

• Allows transmission of very narrow pulses.

• TYPES:PAM-IMPWM-IMPPM-IM

Fig. A PFM–IM optical fiber system employing regenerative baseband recovery

APPLICATION OF INTENSITY MODULATION

• Intensity-modulated radiation therapy (IMRT)